U.S. patent application number 10/450712 was filed with the patent office on 2004-04-15 for process for producing methacrylic acid.
Invention is credited to Oh-Kita, Motomu, Watanabe, Seigo.
Application Number | 20040073062 10/450712 |
Document ID | / |
Family ID | 18858892 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040073062 |
Kind Code |
A1 |
Watanabe, Seigo ; et
al. |
April 15, 2004 |
Process for producing methacrylic acid
Abstract
In a method of producing methacrylic acid by passing a material
gas containing methacrolein, oxygen and water vapor through a
reactor packed with a catalyst containing as the main component a
compound oxide containing molybdenum and phosphorus, a
concentration of methacrolein in the material gas is controlled in
a range of 4 to 6.5 vol %, a molar ratio of the water vapor to the
methacrolein in the material gas is controlled in a range of 1 to
2, and a space velocity of the material gas to the catalyst-packed
layer is controlled in a range of 500 to 750 h.sup.-1, whereby
deterioration of the catalyst is effectively inhibited.
Inventors: |
Watanabe, Seigo; (Hiroshima,
JP) ; Oh-Kita, Motomu; (Hiroshima, JP) |
Correspondence
Address: |
ARMSTRONG, KRATZ, QUINTOS, HANSON & BROOKS, LLP
1725 K STREET, NW
SUITE 1000
WASHINGTON
DC
20006
US
|
Family ID: |
18858892 |
Appl. No.: |
10/450712 |
Filed: |
November 5, 2003 |
PCT Filed: |
December 19, 2001 |
PCT NO: |
PCT/JP01/11117 |
Current U.S.
Class: |
562/535 |
Current CPC
Class: |
B01J 23/002 20130101;
B01J 2523/00 20130101; C07C 51/252 20130101; B01J 2523/00 20130101;
B01J 27/199 20130101; C07C 51/252 20130101; B01J 2523/00 20130101;
B01J 27/19 20130101; B01J 2523/15 20130101; B01J 2523/22 20130101;
B01J 2523/17 20130101; B01J 2523/64 20130101; C07C 57/04 20130101;
B01J 2523/15 20130101; B01J 2523/42 20130101; B01J 2523/55
20130101; B01J 2523/27 20130101; B01J 2523/51 20130101; B01J
2523/842 20130101; B01J 2523/17 20130101; B01J 2523/305 20130101;
B01J 2523/55 20130101; B01J 2523/68 20130101; B01J 2523/51
20130101; B01J 2523/68 20130101 |
Class at
Publication: |
562/535 |
International
Class: |
C07C 051/235; C07C
051/16 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2000 |
JP |
2000-392997 |
Claims
What is claimed is:
1. A method of producing methacrylic acid by passing a material gas
containing methacrolein, oxygen and water vapor through a reactor
packed with a catalyst containing as the main component a compound
oxide containing molybdenum and phosphorus, wherein a concentration
of methacrolein in the material gas is in a range of 4 to 6.5 vol
%, a molar ratio of the water vapor to the methacrolein in the
material gas is in a range of 1 to 2, and a space velocity of the
material gas to the catalyst-packed layer is in a range of 500 to
750 h.sup.-1.
2. The method of producing methacrylic acid according to claim 1
wherein the concentration of methacrolein in the material gas is in
a range of 4.5 to 6 vol %.
3. The method of producing methacrylic acid according to claim 1
wherein the molar ratio of water vapor to methacrolein in the
material gas is in a range of 1.5 to 1.9.
4. The method of producing methacrylic acid according to claim 1
wherein the space velocity of the material gas to the
catalyst-packed layer is in a range of 550 to 700 h.sup.-1.
5. The method of producing methacrylic acid according to claim 1
wherein the catalyst has a composition expressed by the following
general formula (I):
Mo.sub.aP.sub.bCU.sub.cV.sub.dX.sub.eY.sub.fO.sub.g (I) wherein Mo,
P, Cu, V and O represent molybdenum, phosphorus, copper, vanadium
and oxygen, respectively; X represents at least one element
selected from the group consisting of iron, cobalt, nickel, zinc,
magnesium, calcium, strontium, barium, titanium, chromium,
tungsten, manganese, silver, boron, silicon, aluminum, gallium,
germanium, tin, lead, arsenic, antimony, bismuth, niobium,
tantalum, zirconium, indium, sulfur, selenium, tellurium, lanthanum
and cerium; Y represents at least one element selected from the
group consisting of potassium, rubidium, cesium and thallium; a, b,
c, d, e, f and g each represents an atom ratio of each element, and
when a=12, 0.1.ltoreq.b.ltoreq.3, 0.01.ltoreq.c.ltoreq.3,
0.01.ltoreq.d.ltoreq.3, 0.ltoreq.e.ltoreq.3 and
0.01.ltoreq.f.ltoreq.3; and g represents a ratio of an oxygen atom
required for satisfying a valence of each component.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of producing
methacrylic acid, and more particularly, it relates to a method of
producing methacrylic acid by subjecting methacrolein to gas phase
contact oxidation with molecular oxygen.
BACKGROUND ART
[0002] A method of producing methacrylic acid by subjecting
methacrolein to gas phase contact oxidation on a catalyst
comprising a compound oxide containing molybdenum and phosphorous
as essential components is widely known and is also used on an
industrial scale. In this case, methacrylic acid is often produced
at a reaction temperature of 250 to 400.degree. C., using of a
catalyst as a fixed bed.
[0003] The catalyst for use in such a gas phase contact oxidation
reaction is used for a relatively long time, but usually the
catalyst deteriorates with time. Causes of the degradation of the
catalyst include reduction of a catalyst component, sublimation and
flying of a catalyst component, change in a crystalline phase in a
catalyst structure, and the like.
[0004] As for methods for regenerating the thus deteriorated
catalyst, a variety of propositions have been made. For example,
Japanese Patent Laid-open No. 58-156351 discloses a method in which
the deteriorated catalyst is treated at a temperature of 70 to
240.degree. C. in a gaseous stream having a water vapor partial
pressure of 10 vol % or more, and Japanese Patent Laid-open No.
6-7685 discloses a method in which the deteriorated catalyst is
thermally treated under a stream of an oxidizing gas containing 0.1
vol % or more of molecular oxygen at a temperature of 300 to
410.degree. C. for 0.5 to 50 hours. From an industrial viewpoint,
however, it can be considered that it is desired to minimize the
frequency of regenerating the deteriorated catalyst, because it is
quite inconvenient to regenerate the catalyst each time it
deteriorates and the production of methacrylic acid must be
temporarily suspended every such an occasion.
[0005] That is, from an industrial viewpoint, there is desired the
method of producing methacrylic acid while the deterioration of the
catalyst is inhibited as much as possible, rather than the method
of regenerating the deteriorated catalyst.
[0006] Furthermore, as for a catalyst that is resistant to the
deterioration and has a long catalyst life, and a method for
producing the same, numerous propositions have been made, for
example, as in Japanese Patent Laid-open No. 5-31368. However, a
level of the inhibition of the catalyst deterioration is not
necessarily sufficient in industrial practice, and further
technological innovation is desired. Moreover, all of these
propositions only demonstrate that a deterioration rate is slightly
reduced as compared with the catalyst by the conventional
production methods under the same reaction conditions, and they do
not refer to a method for effectively inhibiting the deterioration
of the catalyst by controlling reaction conditions within specific
ranges.
[0007] In addition, as the reaction conditions in producing
methacrylic acid by passing a material gas containing methacrolein,
oxygen and water vapor through a reactor packed with a compound
oxide catalyst containing molybdenum and phosphorus, the following
are known.
[0008] That is, Japanese Patent Laid-open No. 9-75740 describes
that a concentration of methacrolein in a reaction material gas is
in a range of 1 to 10% and a ratio of oxygen to methacrolein is
about 1 to 5, and a space velocity of the material gas is
preferably in a range of 500 to 5,000 h.sup.-1, and water vapor or
the like can be used as a diluting gas. In examples described in
this publication, a material gas having a composition of 4 mol % of
methacrolein, 12 mol % of oxygen, 17 mol % of water vapor and the
balance of nitrogen is passed through a reactor at a space velocity
(STP standard) of 670 h.sup.-1 so that methacrolein may be
subjected to the contact oxidation reaction.
[0009] Furthermore, Japanese Patent Laid-open No. 9-313943
describes that an appropriate contact time of the material gas is 1
to 20 seconds, and as for the composition of the material gas, 0.2
to 4 mols of molecular oxygen and 1 to 20 mols of water vapor are
used with respect to 1 mol of methacrolein. In examples described
in this publication, a material gas having a composition of 5 mol %
of methacrolein, 12 mol % of oxygen, 30 mol % of water vapor and 53
mol % of nitrogen is passed at a space velocity of 1,400 h.sup.-1,
or a material gas having a composition of 3.2 mol % of
methacrolein, 16.4 mol % of oxygen, 19.4 mol % of water vapor and
61 mol % of nitrogen is passed at a space velocity of 2,060
h.sup.-1 so that methacrolein may be subjected to the contact
oxidation reaction.
[0010] However, the reaction conditions described in Japanese
Patent Laid-open No. 9-75740 and Japanese Patent Laid-open No.
9-313943 are reaction conditions in a case where a long-life
catalyst is used, and the publications only disclose very wide
ranges of the material gas compositions and the space velocities.
These publications do not suggest techniques for inhibiting the
deterioration of the catalyst by adjustment of the material gas
composition and the space velocity anywhere. Moreover, in a case
where methacrolein is subjected to the contact oxidation reaction
using the material gas composition and the space velocity
specifically described in these publications, the deterioration of
the catalyst cannot be effectively inhibited.
DISCLOSURE OF THE INVENTION
[0011] An object of the present invention is to provide a novel
method of producing methacrylic acid in which deterioration of a
catalyst is effectively inhibited by controlling a reaction
condition.
[0012] The present invention relates to a method of producing
methacrylic acid by passing a material gas containing methacrolein,
oxygen and water vapor through a reactor packed with a catalyst
containing as the main component a compound oxide containing
molybdenum and phosphorus, wherein a concentration of methacrolein
in the material gas is in a range of 4 to 6.5 vol %, a molar ratio
of the water vapor to the methacrolein in the material gas is in a
range of 1 to 2, and a space velocity of the material gas to the
catalyst-packed layer is in a range of 500 to 750 h.sup.-1.
BEST MODE FOR CARRYING OUT THE INVENTION
[0013] In the present invention, reaction conditions in producing
methacrylic acid by subjecting methacrolein to gas phase contact
oxidation on a catalyst, namely a material gas composition and a
space velocity of a material gas to a catalyst layer, are
controlled within specific limits, whereby deterioration of the
catalyst, particularly reduction in catalyst activity is
effectively inhibited. It is generally considered that a
deterioration rate of the catalyst is roughly dependent on a
frequency in the use of the catalyst, i.e. a reaction amount per
unit time. However, the present inventors have found that in this
reaction, a degradation behavior of the catalyst noticeably varies
depending on the material gas composition and the space velocity of
the material gas to the catalyst layer even if the reaction amount
of methacrolein per unit time per unit the catalyst weight is the
same, and they have also found that the degradation of the catalyst
can be effectively inhibited by controlling the material gas
composition and the space velocity of the material gas to the
catalyst layer within specific limits.
[0014] Hereinafter, a method for producing methacrylic acid of the
present invention will be described.
[0015] A catalyst for use in the present invention comprises a
compound oxide containing molybdenum and phosphorus as essential
components.
[0016] Specifically, the catalyst preferably has a composition
expressed by the following general formula (I):
Mo.sub.aP.sub.bCu.sub.cV.sub.dX.sub.eY.sub.fO.sub.g (I)
[0017] wherein Mo, P, Cu, V and O represent molybdenum, phosphorus,
copper, vanadium and oxygen, respectively; X represents at least
one element selected from the group consisting of iron, cobalt,
nickel, zinc, magnesium, calcium, strontium, barium, titanium,
chromium, tungsten, manganese, silver, boron, silicon, aluminum,
gallium, germanium, tin, lead, arsenic, antimony, bismuth, niobium,
tantalum, zirconium, indium, sulfur, selenium, tellurium, lanthanum
and cerium; Y represents at least one element selected from the
group consisting of potassium, rubidium, cesium and thallium; a, b,
c, d, e, f and g each represents an atom ratio of each element, and
when a=12, 0.1.ltoreq.b.ltoreq.3, 0.01.ltoreq.c.ltoreq.3,
0.01.ltoreq.d.ltoreq.3, 0.ltoreq.e.ltoreq.3 and
0.01.ltoreq.f.ltoreq.3; and g represents a ratio of an oxygen atom
required for satisfying a valence of each component.
[0018] In the present invention, a method of producing the catalyst
comprising the compound oxide containing molybdenum and phosphorus
as the essential components should not be limited to a specific
method, and a variety of conventionally well-known methods such as
a coprecipitation method, an evaporation to dryness method and an
oxide mixing method can be used as long as the components are not
noticeably unevenly distributed specifically, a method can be shown
as an example in which a necessary amount of a raw material
containing the constituent elements of the compound oxide is
appropriately dissolved or suspended in a solvent such as water,
and the resulting mixture solution or aqueous slurry is evaporated
to dryness, ground and molded as required, and then treated with
heat to obtain the catalyst usually, the heat treatment is
preferably carried out under a stream of oxygen, air or nitrogen at
200 to 500.degree. C. for 1 to 30 hours.
[0019] In the present invention, the raw material for use in
preparation of the catalyst is not specifically limited, and
nitrates, carbonates, acetates, ammonium salts, oxides, halides and
the like of the elements can be used in combination. For example,
as a molybdenum raw material, there can be used ammonium
paramolybdate, molybdenum trioxide, molybdic acid, molybdenum
chloride or the like. As a phosphorus raw material, there can be
used orthophosphoric acid, metaphosphoric acid, diphosphorus
pentoxide, pyrophosphoric acid, ammonium phosphate or the like.
[0020] The catalyst for use in the present invention may be an
unsupported molded catalyst, but it may also be supported on an
inert support such as silica, alumina, silica-alumina or silicon
carbide, or may be diluted therewith and then used.
[0021] In the method for producing methacrylic acid of the present
invention, the deterioration of the catalyst is effectively
inhibited by controlling the reaction condition under which
methacrylic acid is produced by subjecting methacrolein to gas
phase contact oxidation in the presence of the catalyst described
above. Hereinafter, the reaction condition of the present invention
will be described in detail.
[0022] The reaction is usually carried out on a fixed bed. A
catalyst layer may have one layer, or two or more layers if the
catalyst layer has two layers, for example, a method can be
employed in which a front layer is packed with a mixture of the
catalyst and the inert support, and a rear layer is packed with the
catalyst alone.
[0023] For the material gas-, a gas containing methacrolein, oxygen
and water vapor is used.
[0024] A concentration of methacrolein in the material gas is in a
range of 4 to 6.5 vol % (4 to 6.5 mol %), and is preferably 4.5 vol
% or more and preferably 6 vol % or less. Generally, if the
concentration of methacrolein is too low, the amount of methacrylic
acid produced per unit time decreases, which is not preferable from
an industrial viewpoint. On the other hand, if the concentration of
methacrolein is too high, a molar ratio of oxygen/methacrolein must
be considerably reduced to put the material gas composition outside
an explosive range, which is not preferable in preventing the
deterioration of the catalyst by reduction. However, it is not just
for this reason that the concentration of methacrolein in the
material gas is strictly limited in the present invention, but
because a sufficient catalyst deterioration inhibiting effect can
be obtained by controlling the concentration of methacrolein within
this range along with various conditions described later.
[0025] The concentration of oxygen in the material gas can be
varied within a broad range, and is preferably 5 mol % or more in
that the deterioration of the catalyst by reduction is sufficiently
inhibited, and preferably 15 mol % or less in terms of safety. If
the concentration of oxygen is too high, a material gas composition
may fall within an explosive range. An oxygen source, air is
preferably used from an economic viewpoint, but air enriched with
pure oxygen, pure oxygen or the like may be used as necessary.
[0026] A molar ratio (volume ratio) of water vapor to methacrolein
in the material gas is in a range of 1 to 2, and is preferably 1.5
or more and preferably 1.9 or less. By controlling the
concentration of water vapor within this range, not only high
selectivity of methacrylic acid, but also a sufficient catalyst
deterioration inhibiting effect can be obtained.
[0027] It is to be noted that the material gas may contain an inert
gas such as nitrogen and carbon dioxide, and may contain impurities
such as a lower saturated aldehyde, which do not substantially
influence the reaction, in a low dose.
[0028] The space velocity of the material gas to the
catalyst-packed layer is in a range of 500 to 750 h.sup.-1, and is
preferably 550 h.sup.-1 or more and preferably 700 h.sup.-1 or
less. If the space velocity is too low, an efficiency of removing
heat of the reaction by the passing of the gas is poor, and
consequently a hot spot (local overheating) is generated in the
catalyst layer to disturb a safe operation on the other hand, if
the space velocity is too high, the deterioration rate of the
catalyst increases even if the concentration of methacrolein in the
material gas is reduced to decrease a reaction amount of
methacrolein per unit time per unit the catalyst weight. That is,
the space velocity is set to be within this range, and then the
material gas composition is set to be within the above range while
considering a production amount of methacrylic acid, safety and the
like, whereby methacrylic acid can be produced while effectively
inhibiting the deterioration of the catalyst.
[0029] The space velocity referred to herein is a value obtained by
dividing a volume (volume at 0.degree. C. and 1 atm) of the
material gas supplied to the catalyst layer per unit time by a
volume of the catalyst layer, and a unit of the space velocity is a
reciprocal of time. For example, when the volume of the catalyst
layer is 1 liter and the material gas is supplied thereto at a rate
of 600 liters per hour, the space velocity is 600 h.sup.-1.
[0030] Furthermore, the volume of the catalyst layer referred to
herein denotes a volume in the reactor substantially occupied by
the catalyst packed in the reactor. It is to be noted that if a
catalyst and an inert support are previously mixed in a part or all
of the catalyst layer or if a catalyst is supported on an inert
support, the volume of the catalyst layer denotes a volume occupied
by a mixture of a catalyst and an inert support. However, if a
front stage and/or a rear stage of the catalyst layer is packed
with an inert support (substantially inert solid material), the
volume of the inert support is not included in the volume of the
catalyst.
[0031] A reaction pressure is preferably in a range of an
atmospheric pressure to a pressure of several atmospheres. A
reaction temperature is preferably in a range of 230 to 400.degree.
C., particularly preferably 250 to 350.degree. C.
EXAMPLES
[0032] Hereinafter, the present invention will be described in
detail with referent to the examples, but the present invention is
not limited to the examples.
[0033] The term "parts" described in the following examples and
comparative examples mean parts by weight. A reaction test analysis
was carried out by a gas chromatography.
[0034] It is to be noted that a conversion of methacrolein and a
selectivity of produced methacrylic acid are defined as
follows:
[0035] the conversion of methacrolein (%)=(B/A).times.100
[0036] the selectivity of methacrylic acid (%)=(C/B).times.100
[0037] wherein A represents the number of moles of supplied
methacrolein, B represents the number of moles of reacted
methacrolein, and c represents the number of moles of produced
methacrylic acid.
Example 1
[0038] 100 parts of ammonium paramolybdate, 2.8 parts of ammonium
matavanadate and 9.2 parts of cesium nitrate were dissolved in 300
parts of pure water. This aqueous solution was stirred while adding
thereto a solution with 8.2 parts of 85 wt % phosphoric acid
dissolved in 10 parts of pure water and a solution with 1.1 parts
of telluric acid dissolved in 10 parts of pure water, and the
resulting mixture was heated to 95.degree. C. Then, a solution with
3.4 parts of copper nitrate, 7.6 parts of ferric nitrate, 1.4 parts
of zinc nitrate and 1.8 parts of magnesium nitrate dissolved in 80
parts of pure water was added. Furthermore, the mixture was stirred
at 100.degree. C. for 15 minutes.
[0039] The resulting slurry was dried, and 2 parts of graphite were
added to 100 parts of this dried material and mixed together, and
was molded into a ring-shaped material having an outer diameter of
5 mm, an inner diameter of 2 mm and a length of 3 mm by a tablet
molder. Then, this tablet-molded product was calcined under a
stream of air at 380.degree. C. for 5 hours to obtain a catalyst
(1).
[0040] The catalyst (1) had a composition of
Mo.sub.12P.sub.1.5Cu.sub.0.3V-
.sub.0.5Fe.sub.0.4Te.sub.0.1Mg.sub.0.15Zn.sub.0.1Cs.sub.1 in an
atom ratio excluding oxygen.
[0041] A mixture of 370 mL of catalyst (1) and 130 mL of alumina
ball having an outer diameter of 5 mm was packed in the material
gas inlet of a steel fixed bed tubular reactor with the inner
diameter of 25.4 mm comprising a heating medium bath, and 1,000 mL
of catalyst (1) was packed in the outlet.
[0042] A material gas containing 5.5 vol % of methacrolein, 10.7
vol % of oxygen, 9.0 vol % of water vapor and 74.8 vol % of
nitrogen was passed through the catalyst layer at a reaction
temperature (temperature of the heating medium bath) of 282.degree.
C. and at a space velocity of 630 hr.sup.-1. The reaction was
carried out in the flow process under atmospheric pressure.
[0043] After 60 minutes from the starting of the reaction, the
reaction product was collected and analyzed, and it was found that
the conversion of methacrolein was 83.7%, and the selectivity of
methacrylic acid was 83.8%.
[0044] The reaction was further continued for 2,400 hours under the
conditions described above, and the reaction product was collected
and analyzed, and it was found that the conversion of methacrolein
was 83.6%, and the selectivity of methacrylic acid was 83.8%. The
catalyst suffered almost no deterioration even after the reaction
was carried out for 2,400 hours under these conditions.
Example 2
[0045] The reaction was carried out in the same manner as Example 1
except that a material gas containing 4.9 vol % of methacrolein,
10.3 vol % of oxygen, 9.0 vol % of water vapor and 75.8 vol % of
nitrogen was passed through the catalyst layer at a reaction
temperature (temperature of the heating medium bath) of 284.degree.
C. and at a space velocity of 710 hr.sup.-1.
[0046] After 60 minutes from the starting of the reaction, the
reaction product was collected and analyzed, and it was found that
the conversion of methacrolein was 84.1%, and the selectivity of
methacrylic acid was 84.0%.
[0047] The reaction was further continued for 2,400 hours under the
conditions described above, and the reaction product was collected
and analyzed, and it was found that the conversion of methacrolein
was 83.9%, and the selectivity of methacrylic acid was 84.1%. The
catalyst suffered almost no deterioration even after the reaction
was carried out for 2,400 hours under these conditions.
<Comparative Example 1>
[0048] The reaction was carried out in the same manner as Example 1
except that a material gas containing 3.5 vol % of methacrolein,
8.8 vol % of oxygen, 6.5 vol % of water vapor and 81.2 vol % of
nitrogen was passed through the catalyst layer at a reaction
temperature (temperature of the heating medium bath) of 286.degree.
C. and at a space velocity of 1,000 hr.sup.-1.
[0049] After 60 minutes from the starting of the reaction, the
reaction product was collected and analyzed, and it was found that
the conversion of methacrolein was 84.0%, and the selectivity of
methacrylic acid was 84.2%.
[0050] The reaction was further continued for 2,400 hours under the
conditions described above, and the reaction product was collected
and analyzed, and it was found that the conversion of methacrolein
was 81.2%, the selectivity of methacrylic acid was 84.4%, and the
catalyst activity decreased significantly.
<Comparative Example 2>
[0051] The reaction was carried out in the same manner as Example 2
except that the material gas was changed to a material gas
containing 4.9 vol % of methacrolein, 10.3 vol % of oxygen, 14.7
vol % of water vapor and 70.1 vol % of nitrogen.
[0052] After 60 minutes from the starting of the reaction, the
reaction product was collected and analyzed, and it was found that
the conversion of methacrolein was 83.8%, and the selectivity of
methacrylic acid was 83.8%.
[0053] The reaction was further continued for 2,400 hours under the
conditions described above, and the reaction product was collected
and analyzed, and it was found that the conversion of methacrolein
was 82.1%, the selectivity of methacrylic acid was 83.3%, and the
catalyst activity decreased significantly.
<Comparative Example 3>
[0054] The reaction was carried out in the same manner as Example 2
except that the material gas was changed to a material gas
containing 4.9 vol % of methacrolein, 10.3 vol % of oxygen, 2.0 vol
% of water vapor and 82.8 vol % of nitrogen.
[0055] After 60 minutes from the starting of the reaction, the
reaction product was collected and analyzed, and it was found that
the conversion of methacrolein was 82.5%, and the selectivity of
methacrylic acid was 83.1%.
[0056] The reaction was further continued for 2,400 hours under the
conditions described above, and the reaction product was collected
and analyzed, and it was found that the conversion of methacrolein
was 80.1%, the selectivity of methacrylic acid was 83.5%, and the
catalyst activity decreased significantly.
Example 3
[0057] 100 parts of molybdenum trioxide, 3.2 parts of vanadium
pentoxide and 6.7 parts of 85 wt % phosphoric acid were mixed with
800 parts of pure water. The resulting mixture was heated and
stirred under reflux for 3 hours, and thereafter 0.5 parts of
copper oxide, 0.7 parts of boric acid and 1.2 parts of germanium
dioxide were added, and the resulting mixture was heated and
stirred under reflux for 2 hours. The resulting slurry was cooled
down to 50.degree. C., and thereafter a solution with 11.2 parts of
cesium bicarbonate dissolved in 30 parts of pure water was added,
and the resulting slurry was stirred for 15 minutes. Then, a
solution with 10 parts of ammonium nitrate dissolved in 30 parts of
pure water was added, and the resulting slurry was stirred for 15
minutes.
[0058] The resulting slurry was dried, and 2 parts of graphite were
added to 100 parts of this dried material and mixed together, and
was molded into a ring-shaped material having an outer diameter of
5 mm, an inner diameter of 2 mm and a length of 3 mm by a tablet
molder. Then, this tablet-molded product was calcined under a
stream of air at 380.degree. C. for 5 hours to obtain a catalyst
(2).
[0059] The catalyst (2) had a composition of
Mo.sub.12P.sub.1Cu.sub.0.1V.s- ub.0.6Ge.sub.0.2B.sub.0.2Cs.sub.1 in
an atom ratio excluding oxygen.
[0060] A mixture of 150 mL of catalyst (2) and 90 mL of alumina
ball having an outer diameter of 5 mm was packed in the material
gas inlet of a steel fixed bed tubular reactor with the inner
diameter of 25.4 mm comprising a heating medium bath, a mixture of
200 mL of catalyst (2) and 40 mL of alumina ball having an outer
diameter of 5 mm was packed in the central part, and 1,020 mL of
catalyst (2) was packed in the outlet.
[0061] A material gas containing 5.2 vol % of methacrolein, 10.5
vol % of oxygen, 9.0 vol % of water vapor and 75.3 vol % of
nitrogen was passed through the catalyst layer at a reaction
temperature (temperature of the heating medium bath) of 282.degree.
C. and at a space velocity of 670 hr.sup.-1. The reaction was
carried out in the flow process under atmospheric pressure.
[0062] After 60 minutes from the starting of the reaction, the
reaction product was collected and analyzed, and it was found that
the conversion of methacrolein was 85.1%, and the selectivity of
methacrylic acid was 85.0%.
[0063] The reaction was further continued for 2,400 hours under the
conditions described above, and the reaction product was collected
and analyzed, and it was found that the conversion of methacrolein
was 85.0%, and the selectivity of methacrylic acid was 85.0%. The
catalyst suffered almost no deterioration even after the reaction
was carried out for 2,400 hours under these conditions.
INDUSTRIAL APPLICABILITY
[0064] According to the present invention, in a method of producing
methacrylic acid which comprises subjecting methacrolein to gas
phase contact oxidation with molecular oxygen using a reactor
packed with a catalyst comprising a compound oxide containing
molybdenum and phosphorus as essential components, deterioration of
the catalyst can be effectively inhibited.
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